Image forming apparatus that determines a control target temperature based on a history of a coverage ratio

Abstract

When an image forming portion continuously forms a toner image on a plurality of recording materials, an acquiring portion, which acquires information on the toner on the recording materials from the image information, acquires a coverage ratio, which is a ratio of an image portion, that is, a toner laid-on portion in a predetermined region of the recording material, with respect to the predetermined region, for a plurality of recording materials, and an power control portion controls the power supplied to a heating element of a heater in a fixing portion for each of the plurality of recording materials based on a control target temperature, which is determined by correcting a reference target temperature in the predetermined region by a correction amount reflecting the history of the coverage ratio in the plurality of recording materials.

What is claimed is: 
     
       1. An image forming apparatus comprising:
 an image forming portion configured to form a toner image on a recording material in accordance with an image information; 
 a fixing portion configured to fix the toner image to the recording material, the fixing portion includes a tubular film contacting the toner image on the recording material and a heating unit, configured to heat the toner image through the film, being in contact with an inner surface of the film; 
 a temperature detecting portion configured to detect a temperature of the fixing portion; 
 a power control portion configure to controls a power to be supplied to the heating unit so that the temperature detected by the temperature detecting portion is maintained at a target temperature; and 
 an acquiring portion configured to acquire an information according to a toner image area on the recording material, 
 wherein when the image forming portion continuously forms the toner image on a plurality of recording materials, the power control portion sets the target temperatures for each of the plurality of recording materials in accordance with a history of the toner image area in the plurality of recording materials. 
 
     
     
       2. The image forming apparatus according to  claim 1 ,
 wherein the fixing portion includes a roller configured to form a fixing nip portion for nipping and conveying the recording material in cooperation with the heating unit through the film. 
 
     
     
       3. The image forming apparatus according to  claim 2 ,
 wherein the heating unit includes a heater which generates heat by power to be supplied. 
 
     
     
       4. An image forming apparatus comprising:
 an image forming portion which forms a toner image on a recording material based on image information; 
 a fixing portion which includes a heater constituted of a substrate and a heating element disposed on the substrate, and fixes a toner image formed on a recording material to the recording material using the heat of the heater; 
 a temperature detecting portion which detects the temperature of the heater; 
 a power control portion which controls power to be supplied to the heating element based on the temperature detected by the temperature detecting portion; and 
 an acquiring portion which acquires information on the toner on the recording material from the image information; 
 wherein when the image forming portion continuously forms a toner image on a plurality of recording materials; 
 the acquiring portion acquires; from the image information; a coverage ratio; which is a ratio of an image portion that is a toner laid-on portion in a predetermined region of the recording material to the predetermined region; for the plurality of recording materials; and 
 the power control portion controls the power supplied to the heating element for each of the plurality of recording materials based on a control target temperature; which is determined by correcting a reference target temperature in the predetermined region with a correction amount reflecting a history of the coverage ratio in the plurality of recording materials. 
 
     
     
       5. The image forming apparatus according to  Claim 1 ,
 wherein the acquiring portion acquires, from the image information, an average print percentage, which is an average value of toner laid-on level per unit area in the image portion in the predetermined region of the recording material, 
 wherein the correction amount is a sum of: an integrated temperature correction amount that is set based on the coverage ratio and the average print percentage in the heated recording materials out of the plurality of recording materials, and the temperature correction amount in the recording materials to be heated. 
 
     
     
       6. The image forming apparatus according to  Claim 5 , wherein when the sum is outside a range of the correction amount specified by an upper limit value and a lower limit value, which are set based on the coverage ratio and the average print percentage of the recording materials to be heated, the correction amount is adjusted to be within the range. 
     
     
       7. The image forming apparatus according to  Claim 4 ,
 wherein the acquiring portion acquires, from the image information, a maximum print percentage which is the maximum value of the toner laid-on level per unit area in the predetermined region of the recording material, 
 wherein the reference target temperature is set based on the maximum print percentage of the recording material to be heated. 
 
     
     
       8. The image forming apparatus according to  Claim 4 ,
 wherein the predetermined region is a region of a recording material corresponding to one of a plurality of regions generated by dividing a heating region of the heater in a direction perpendicular to a transporting direction of the recording material, 
 wherein the power control portion controls power supplied to the heating element for each of the plurality of recording materials, based on the corrected control target temperature that is highest in all the predetermined regions corresponding to the heating region. 
 
     
     
       9. The image forming apparatus according to  Claim 4 ,
 wherein the fixing portion is disposed so that the plurality of heating elements are arranged on the substrate in the longer direction of the substrate, 
 wherein the predetermined region is a region of the recording material corresponding to one of a plurality of heating regions to be heated by the plurality of heating elements, 
 wherein the power control portion controls, for each of the plurality of recording materials, power supplied to the heating element for each of the plurality of heating regions based on a control target temperature, which is determined by indiVidually correcting the reference target temperature by the correction amount in each of the plurality of predetermined regions corresponding to the plurality of heating regions. 
 
     
     
       10. The image forming apparatus according to  claim 1 , wherein the fixing portion includes a tubular film,
 wherein the tubular film rotates with an inner surface thereof contacting the heater, and 
 an image on the recording material is heated via the film.